Chromosome Replication and Segregation

Abstract

This chapter reviews our current understanding of bacterial DNA replication and chromosome partitioning in Bacillus subtilis and makes comparisons to Escherichia coli and other organisms where appropriate. Bacterial chromosome replication initiates once per cell division cycle in response to a signal that is tightly coupled to cell mass. Although the helicase function of B. subtilis DnaC has not yet been confirmed biochemically, two types of dna(TS) mutations, defective in initiation and elongation, map to dnaC. Strong interaction between the helicase and the primase has been demonstrated in Bacillus stearotrtermophilus. The current understanding of bacterial chromosome partitioning can be simplified into three steps: (i) origin region separation and repositioning, (ii) overall chromosome organization and compaction, and (iii) terminus region separation. This final step includes chromosome decatenation, chromosome dimer-to-monomer resolution when necessary, and movement of the termini to either side of midcell before completion of medial division. The structural maintenance of chromosomes (SMC) protein family is well conserved and is important for chromosome segregation in bacteria, archaea, and eukaryotes. Both B. subtilis and E. coli have proteins that appear to be involved in postseptational chromosome partitioning. These proteins, SpoIIIE and FtsK, respectively, have domains that are homologous to the DNA translocation domains of proteins involved in conjugative plasmid transfer. In B. subtilis and Caulobacter crescentus, SMC functions in chromosome partitioning presumably by affecting chromosome organization and compaction. All organisms seem to have proteins that contribute to chromosome folding and compaction.